Re: [PATCH v4 7/8] v4l: Add signal lock status to source change events

[Steve Longerbeam]

On 11/14/2016 11:19 AM, Steve Longerbeam wrote:
> On 11/14/2016 03:36 AM, Hans Verkuil wrote:
> > On 08/03/2016 08:03 PM, Steve Longerbeam wrote:
> > > Add a signal lock status change to the source changes bitmask.
> > > This indicates there was a signal lock or unlock event detected
> > > at the input of a video decoder.
> > >
> > > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
> > > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
> > >
> > > ---
> > >
> > > v4:
> > > - converted to rst from DocBook
> > >
> > > v3: no changes
> > > v2: no changes
> > > ---
> > >   Documentation/media/uapi/v4l/vidioc-dqevent.rst | 9 +++++++++
> > >   Documentation/media/videodev2.h.rst.exceptions  | 1 +
> > >   include/uapi/linux/videodev2.h                  | 1 +
> > >   3 files changed, 11 insertions(+)
> > >
> > > diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst 
> > > b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > > index 73c0d5b..7d8a053 100644
> > > --- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > > +++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > > @@ -564,6 +564,15 @@ call.
> > >         an input. This can come from an input connector or from a video
> > >         decoder.
> > >   +    -  .. row 2
> > > +
> > > +       -  ``V4L2_EVENT_SRC_CH_LOCK_STATUS``
> > > +
> > > +       -  0x0002
> > > +
> > > +       -  This event gets triggered when there is a signal lock or
> > > +      unlock detected at the input of a video decoder.
> > > +
> > >     Return Value
> > >   ============
> > > diff --git a/Documentation/media/videodev2.h.rst.exceptions 
> > > b/Documentation/media/videodev2.h.rst.exceptions
> > > index 9bb9a6c..f412cc8 100644
> > > --- a/Documentation/media/videodev2.h.rst.exceptions
> > > +++ b/Documentation/media/videodev2.h.rst.exceptions
> > > @@ -453,6 +453,7 @@ replace define V4L2_EVENT_CTRL_CH_FLAGS 
> > > ctrl-changes-flags
> > >   replace define V4L2_EVENT_CTRL_CH_RANGE ctrl-changes-flags
> > >     replace define V4L2_EVENT_SRC_CH_RESOLUTION src-changes-flags
> > > +replace define V4L2_EVENT_SRC_CH_LOCK_STATUS src-changes-flags
> > >     replace define V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ 
> > > v4l2-event-motion-det
> > >   diff --git a/include/uapi/linux/videodev2.h 
> > > b/include/uapi/linux/videodev2.h
> > > index 724f43e..08a153f 100644
> > > --- a/include/uapi/linux/videodev2.h
> > > +++ b/include/uapi/linux/videodev2.h
> > > @@ -2078,6 +2078,7 @@ struct v4l2_event_frame_sync {
> > >   };
> > >     #define V4L2_EVENT_SRC_CH_RESOLUTION        (1 << 0)
> > > +#define V4L2_EVENT_SRC_CH_LOCK_STATUS        (1 << 1)
> > >     struct v4l2_event_src_change {
> > >       __u32 changes;
> > Quoting from an old (July) conversation about this:
> >
> > > > > I'm not entirely sure I like this. Typically losing lock means 
> > > > > that this event
> > > > > is triggered with the V4L2_EVENT_SRC_CH_RESOLUTION flag set, and 
> > > > > userspace has
> > > > > to check the new timings etc., which will fail if there is no lock 
> > > > > anymore.
> > > > >
> > > > > This information is also available through ENUMINPUT.
> > > > >
> > > > > I would need to know more about why you think this is needed, 
> > > > > because I don't
> > > > > see what this adds.
> > > Hi Hans,
> > >
> > > At least on the ADV718x, a source resolution change (from an
> > > autodetected video
> > > standard change) and a signal lock status change are distinct events.
> > > For example
> > > there can be a temporary loss of input signal lock without a change in
> > > detected
> > > input video standard/resolution.
> > OK, but what can the application do with that event? If the glitch 
> > didn't
> > affect the video, then it is pointless.
>
> Hi Hans, that's just it, for i.mx6 it does affect video. On i.mx6 a 
> temporary
> loss of signal from the adv7180 often results in a "split image", or 
> rolling
> image from captured frame to the next, and the only way to recover
> from this failure is to restart the pipeline (stream off -- stream 
> on). So
> the application needs to be informed of this temporary loss of signal
> event in order to restart streaming.
>
>
> > If the lock is lost, then normally you loose video as well. If not, then
> > applications are not interested in the event.
>
> Yes, the lost lock causes a temporary or permanent loss of video,
> but with no other indications from the adv7180 (such as a detected
> video standard change). And on i.mx6, the lost lock often (actually
> usually) causes a split or rolling image.

Also it seems the sequence of actions from the application due to a
SRC_CH_LOCK_STATUS event would be in line with the action due to
SRC_CH_RESOLUTION. In other words for SRC_CH_RESOLUTION,
the app requests an update on the detected video standard via
QUERYSTD, and for SRC_CH_LOCK_STATUS, it requests an update
on input status (ENUMINPUTS).

Steve